1. Field of Art
The disclosure generally relates to the field of memory devices, and more particularly, optimization for protected areas of solid state memory devices.
2. Description of the Related Art
Today, Secure Digital (SD) cards are in wide use for many storage applications including audio (MP3 players), pictures (digital cameras), and full motion video (camcorders and HD camcorders). The SD card provides an acceptable portable storage medium to transfer unprotected content between different devices, especially for the video capture devices mentioned above. The content stored on SD cards can be transferred or archived to devices with larger storage capacities and additional processing capabilities. One such additional processing capability allows consumers to create and manage a digital archive of consumer generated content.
Consumers are familiar with the storage capabilities, but there are a very few applications which take advantage of the security (the S in Secure Digital) features of the SD card. Today's applications that use the security features enable digital rights management (DRM) to protect the content from copying or other forms of piracy and theft. Examples of DRM applications include still images and full-motion video (1-seg and GreenPlay by MOD Systems Incorporated). DRM protected content on the aforementioned SD cards cannot be archived easily. The DRM protection must remain intact during generation, transfer, and archival, often tied directly to the physical SD media on which it was originally stored.
The DRM specification and processing require access to both the secure and user areas of an SD card. Specific linkages between the files on the secure area and the files on the user area are determined by the DRM specification. For SD cards, there are multiple DRM specifications currently in existence for different applications. Three of particular DRM types are SD-bind, SD-Video, and SDSD-Video.
When accessing the secure area, a mutual authentication (e.g., authenticated key exchange (AKE)) process is necessary prior to accessing the secure area. This process can take 10 ms or more for each secure area access and is highly dependent on the physical implementation of the SD cards themselves. There are three types of secure accesses available: read, write, and erase. Each time a mutual authentication is completed, a single secure access can be accomplished. If an operation requires more than one access (for examples, reading a directory entry or reading different files) or more than one type of access (erase, read, write), a mutual authentication is required for each access. The 10+ milliseconds (“ms”) time is therefore additive, if not multiplicative, and reduces the rate at which the SD cards can be programmed.
This problem is exemplified by applications using SD card security. For example, several companies are preloading movie content on microSD cards to playback in CE devices. Preloading means that content is loaded on to the SD card prior to packaging. Other companies are loading content on-demand in a retail environment, a form of manufacturing on demand. Both processes are subject to speed degradation associated with the mutual authentication process.
Typical process overhead for preloading consists of 25 AKE operations for SD-Bind. More AKE operations are required for manufacturing on demand if the SD card is not in an “initial” state containing only the file systems. More operations are needed for SD-Video and SDSD-Video as the number of AKE operations is also dependent on the content to be protected. AKE for SDSD-Video is approximately 100 operations. Moving content from one SD device to another can range from 70 to almost 150 operations. Using a 10 ms average time for a single AKE operation, this process can add 250 ms to the manufacturing cycle time for secure operations alone. Using an SD card with a 10 MB/s throughput (a class 10 SD card) and a content size of 500 MB, content write time is approximately 50 second (“s”) for content plus 250 ms for secure operations leaving the total time to write the content at 50.25 s.